As demand for analytical methods for quickly analyzing components contained in samples in the field such as food safety, drug quality control, medical diagnosis, environmental analysis, forensic medicine, explosive detection, rapid detection of a chemical/biological agent, mass spectrometry (MS) for various field detection has been developed.
For example, mass spectrometry using an ambient ionization method is appropriate to be developed as mobile equipment because a sample may not be preprocessed or may be directly analyzed in the field by simply preparing the sample. Since desorption electrospray ionization (DESI) and direct analysis in real time ionization method were developed, a mass spectrometer using an ionization method combined with various other principles have been developed. The ambient ionization method may be divided into two groups: spray-based ionization and plasma-based ionization.
The spray-based ionization method has ionization characteristics similar to electrospray ionization (ESI), and DESI is a typical ionization method. Since polyvalent ions are easily produced, the spray-based ionization method has an advantage in that it is able to analyze various materials ranging from a low molecular weight compound with a small molecular weight to a biopolymer such as protein. However, since a solvent is used and the solvent is injected in the form of liquid particles to an introduction part of the mass spectrometer, possibilities of contamination of the introduction part and a reduction in ion signals due to a matrix effect during ionization may not be excluded.
The plasma-based ionization has ionization characteristics similar to atmospheric pressure chemical ionization (APCI), and DART ionization method is a typical plasma-based ionization method. Specifically, metastable chemical species or primary ions produced by plasma produces gaseous reagent ions for ionizing a material, and the gaseous reagent ions ionize a material present on a surface or a vaporized material. The plasma-based ionization is mainly advantageous for ionization of materials which generate monovalent ions and are well vaporized. Since the plasma-based ionization does not use a solvent or uses a minimum amount, if ever, the plasma-based ionization has an advantage as an ionization method of field detection equipment for directly analyzing a sample without preprocessing, but it is disadvantageous in that ionizable components are limited. In particular, since it is difficult to detect a component with low volatility, it may widen a detection range by developing various methods for heating a surface of a sample, but a fundamental limitation has not overcome. The plasma-based ionization method includes a plasma assisted desorption ionization (PADI), dielectric barrier discharge ionization (DBD), flowing atmosphere-pressure afterglow (FAPA), low temperature plasma (LTP), and the like. The plasma-based ionization method exhibits different characteristics according to whether DC or AC plasma power is used, a voltage and a frequency of discharged power, design of an electrode and a plasma device, and a type and a flow rate of a plasma gas, but it has only an effect of partial heating based on plasma illustrating a relatively high temperature in a portion but has difficulty in analyzing a component with low volatility.